<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .d1{
            width:200px;
            height: 200px;
            background:red;
             /*可以设置边框、内边距、内容  */
            /*border:1px solid red;*/
            padding:1px;

        }
        .d2{
            width:100px;
            height: 100px;
            background:blue;
            margin-top:100px;
        }
    </style>
</head>
<body>
    <div class="d1">
        <div class="d2"></div>
    </div>
</body>
</html>